204 Sir W, Eamsay and Mr. F. Soddy. Radioactivity [July 28, 



forms nitrous fumes when acted upon by the radium rays or by 



light. 



Becquerel* mentions the case of mercuric chloride which in presence 

 of oxalic acid is decomposed by light rays, and by radium rays. 



*" Experiments in Eadioactivity, and the Production of Helium 

 from Kadium." By Sir WILLIAM EAMSAY, K.C.B., F.E.S., 

 and FREDERICK SODDY, M.A. Eeceived July 28, 1903. 



1. Experiments on the Radioactivity of the Inert Gases of the Atmosphere. 



Of recent years many investigations have been made by Elster and 

 Geitel, Wilson, Strutt, Eutherford, Cooke, Allen, arid others on the 

 spontaneous ionisation of the gases of the atmosphere and on the excited 

 radioactivity obtainable from it. It became of interest to ascertain 

 whether the inert monatomic gases of the atmosphere bear any share 

 in these phenomena. For this purpose a small electroscope contained 

 in a glass tube of about 20 c.c. capacity, covered in the interior with 

 tin-foil, was employed. After charging, the apparatus if exhausted 

 retained its charge for thirty-six hours without diminution. Admission 

 of air caused a slow discharge. In similar experiments with helium, 

 neon, argon, krypton, and xenon, the last mixed with oxygen, the rate 

 of discharge was proportional to the density and pressure of the gas. 

 This shows that the gases have no special radioactivity of their own, 

 and accords with the explanation already advanced by these investi- 

 gators that the discharging power of the air is caused by extraneous 

 radioactivity. 



Experiments were also made with the dregs left after liquefied air 

 had nearly entirely evaporated, and again with the same result ; no 

 increase in discharging power is produced by concentration of a possible 

 radioactive constituent of the atmosphere. 



2. Experiments on the Nature of the Radioactive Emanation from Radium. 



The word emanation originally used by Boyle (" substantial emana- 

 tions from the celestial bodies") was resuscitated by Eutherford 

 to designate definite substances of a gaseous nature continuously 

 produced from other substances. The term was also used by Eussell 

 ("emanation from hydrogen peroxide") in much the same sense. 

 If the adjective "radioactive" be added, the phenomenon of 

 Eutherford is distinguished from the phenomena observed by Eussell. 



* Ibid., vol. 133, 1901, p. 709. 



